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Subjects

Abstract

Borneo’s diverse ecosystems, which are typical humid tropical conditions, are deteriorating rapidly, as the area is experiencing recurrent large-scale wildfires, affecting atmospheric composition1,2,3,4 and influencing regional climate processes5,6. Studies suggest that climate-driven drought regulates wildfires2,7,8,9, but these overlook subsurface processes leading to hydrological drought, an important driver. Here, we show that models which include hydrological processes better predict area burnt than those solely based on climate data. We report that the Borneo landscape10 has experienced a substantial hydrological drying trend since the early twentieth century, leading to progressive tree mortality, more severe than in other tropical regions11. This has caused massive wildfires in lowland Borneo during the past two decades, which we show are clustered in years with large areas of hydrological drought coinciding with strong El Niño events. Statistical modelling evidence shows amplifying wildfires and greater area burnt in response to El Niño/Southern Oscillation (ENSO) strength, when hydrology is considered. These results highlight the importance of considering hydrological drought for wildfire prediction, and we recommend that hydrology should be considered in future studies of the impact of projected ENSO strength, including effects on tropical ecosystems, and biodiversity conservation.

Acknowledgements

This present study was completed with support of DIKTI Scholarship (contract no: 4115/E4.4/K/2013) and project SPIN-JRP-29 granted by Royal Netherlands Academy of Arts and Sciences (KNAW). It contributes to WIMEK-SENSE and UNESCO IHP-VIII programme FRIEND-Water. D.M.’s time is supported by USAID grant through SWAMP.

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Contributions

M.T. and H.A.J.V.L. conceived and implemented the research. M.T. and P.J.J.F.T. performed data analysis. M.T. and H.A.J.V.L. wrote the initial version of the paper. M.T. performed model output analysis and generated all figures. All authors contributed to interpreting results, discussion of the associated dynamics and improvement of this paper.